Various flying-plate change printing machines are known, in which alternately used plate cylinders are provided, selectively engageable with an offset or blanket cylinder. The referenced application, assigned to the assignee of the present invention, U.S. patent application Ser. No. 07/706,883, filed May 29, 1991, Knauer et al, describes such a machine, which is suitable for perfecting printing, and in which the plate cylinders are retained in fixed axial position within the printing machine, and the blanket cylinders are, selectively, engageable, with either one of a pair of plate cylinders, so that the other pair of plate cylinders can have their plates changed, or with neither one of the plate cylinders. The bearings for the rubber blanket cylinders, thus, are so constructed that they may have three positions two print-ON positions for engagement with the respective plate cylinder pair, and a throw-OFF position.
The position change of the blanket cylinders, in accordance with the disclosure of the applification, utilizes pneumatic positioning apparatus which engage on eccentric bearings. Customarily, the pneumatic positioning apparatus includes pneumatic cylinder-piston units which are coupled by suitable links to the eccenter bearing, to shift the position of the eccentric bearing and thus appropriately positioning the blanket cylinder, retained within the bearing.
It has been found that, during printing operation, the blanket cylinders engaged with the plate cylinders are subjected to oscillating forces which are transferred via the linkage to the air cushion of the pneumatic piston-cylinder unit. This feedback causes a variation in the engagement pressure of the rubber blanket cylinder with the respective plate cylinder; a uniform engagement pressure, thus, is not ensured.